1. Field of the Invention
This invention relates to an electrophotographic reproduction process and in particular to such an electrophotographic reproduction process capable of forming a reproduced image of excellent quality without causing a forced fatigue to a photosensitive member even if the photosensitive member is used in repeated cycles.
2. Description of the Prior Art
In electrophotographic reproduction machines, the same photosensitive member including a photoconductive layer is repetitively used to form a reproduced image thereon, and while such a photosensitive member is subjected to process steps including uniform charging, image exposure, developing, transfer, cleaning and discharging, charges are trapped in the photosensitive member so that the surface potential of the photosensitive member fluctuates and the effectiveness of uniform charging becomes reduced. Consequently, the potential of the image area in effect decreases and thus the contrast between the light portion (background area) and the dark portion (image area) of an original image deteriorates. Furthermore, in the case where the next following cycle of reproduction operation is to be initiated after elapsing a relatively long resting period subsequent to the last operation, the trapped charges are gradually released during such a resting period so that the photosensitive member is temporarily restored to its original condition. As a result, reproduced images of high contrast may again be obtained only during the first few cycles and contrast again deteriorates as the reproduction cycle is repeated further thereby causing unstability in the quality of reproduced images.
The above-described phenomenon is often termed as light fatigue and it is well known that such a phenomenon is generally encountered in the case where use is made of a photosensitive member which is comprised of amorphous As.sub.2 Se.sub.3 and the like. In order to cope with such a light fatigue phenomenon, one approach is to cause the photosensitive member forcibly fatigued to a sufficient level prior to the initiation of reproduction process thereby allowing to obtain a reproduced image of constant quality, as disclosed in the Japanese Patent Publication, No. 49-4337. Another approach is to carry out a dead cycle prior to the initiation of reproduction process in which the photosensitive member is subjected to blanket illumination by a light source for image exposure.
However, these prior art methods for obtaining reproduced images of constant quality by the application of forced fatigue suffer from various disadvantages. For example, the time period required to carry out such a forced fatigue step contributes to prolong the entire reproduction process thereby slowing down the process. And the prior art methods are rather difficult to implement and consumes a relatively large amount of power.